irjet-experimental investigation of heat transfer characteristics of pulsating turbulent flow in a...

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072

2015, IRJET.NET- All Rights Reserved Page 487

Experimental investigation of heat transfer characteristics of pulsating

turbulent flow in a pipe

Siddhanath V. Nishandar1, R.H.Yadav2 *Student, Dr.JJMCOE Jaysingpur, Maharashtra, India

2Asst. Professor, Dr.JJMCOE Jaysingpu, Maharashtra, India ---------------------------------------------------------------------***---------------------------------------------------------------- Abstract - There are many engineering practical situations where heat is being transferred under

conditions of pulsating and reciprocating flows such as

the operation of modern power producing facilities and

industrial equipment used in metallurgy, aviation,

chemical and food technology. The performance of this

equipment in thermal engineering applications is

affected by the pulsating flow parameters.

The objective of the present work is to

evaluate experimentally the heat transfer

characteristics of pulsatile turbulent flow in a pipe. The

effect of pulsation frequency, location of pulsation

mechanism on the heat transfer characteristics in

pulsatile flow has been evaluated. At the same time

pulsating flow visualization with smoke generation has

been done. The effect of flow pulsation on average and

local heat transfer coefficient has been experimentally

evaluated.

The result shows that, the values of mean

heat transfer coefficient are increases if pulsation is

created in flow of air but the local heat transfer

coefficient either increased or decreased with

increasing the value of pulsation frequency. The values

of mean Nusselt number are increases if pulsation is

created in flow but local Nusselt number either

increases or decreases with increasing the pulsation

frequency. The effective way of increasing the average

heat transfer coefficient is by locating the pulsation

mechanism at the downstream. The maximum

enhancement occurred in average Nusselt number is 38

% at pulsation frequency of 3.33 Hz as compared with

plain tube.

Key Words: Heat transfer enhancement, pulsation,

Turbulent flow, Pipe flow

1. Introduction

Conventionally, uniform fluid flow system is used

in many fluid flow and heat transfer systems in

conventional size as well as micro channel systems. Thus,

many studies do exist in literature that deals with such

systems which helped to understand the thermo-

hydrodynamics of single phase as well as two-phase

systems. Additionally, two more types of fluid flow that

find application in many engineering systems (a)

oscillating flow (or oscillatory flow), and (b) pulsating flow

(or pulsatile flow). When there is no net mean velocity of

the fluid in any direction and it is only oscillating back and

forth about a fixed point with a superimposed frequency

only then the flow is called oscillating flow. Where in case

of pulsating flow, an oscillating velocity is superimposed

with the one directional translational velocity. Therefore

in pulsating flow time-average velocity is non-zero

whereas in oscillating flow time-average velocity is zero

over any particular period of cycle at any instant. This type

of flow mainly characterized by two parameters namely (i)

frequency of oscillation, f (or Womersley number, Wo),

and (ii) amplitude of oscillation (A). Because of rapid

motion, convective heat transfer may increase in such

cases. The effect of pulsations on heat transfer is an

interesting problem for researchers due to its wide

occurrences in many real time situations at macro as well

as mini/micro level.

The enhancement and determination of pipe wall

convective heat transfer characteristics has likely been

one of the most interesting engineering aspects of heat

transfer research. Different methods to enhance the heat

transfer coefficient were developed. Pulsating flow which

is defined as flow with periodic fluctuations of the bulk

mass flow rate may have the same influence on enhancing

the heat transfer coefficients.

2. Literature Review

Several researchers have presented experimental,

analytical and numerical studies on the effect of pulsation

on heat transfer characteristics.

The characteristic of laminar pulsating flow inside

tube under uniform wall heat flux have been

experimentally investigated by Habbib et al.[12]. It is

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 02 Issue: 01 | Jan-2015 www.irjet.net p-ISSN: 2395-0072


reported that an increase and reduction in Nusselt number

are observed, depending on the values of both the

frequency and Reynolds number. Zheng et al [8] used self-

oscillator in their investigations and concluded that the

convective heat transfer rate is greatly affected by the

configuration of the resonator. An analytical study on

laminar pulsating flow in a pipe by Faghri et al. [13]

reported that higher heat transfer rates are produced.

They related that to the interaction between the velocity

and temperature oscillation which introduces an extra

term in the energy equation that reflects the effect of

pulsations. On the other hand,

Tie-Chang et al. [14] reported that the pulsation

has no effect on the time averaged Nusselt number. An

investigation to pulsating pipe flow with different

amplitude was carried out by Guo et al. [15]. In case of

small amplitudes, both heat transfer enhancement and

reduction were detected, depending on the pulsation

frequency. However, with large amplitudes, the heat

transfer rates are always enhanced. Hemeada et al. [16]

analyzed heat transfer in laminar incompressible

pulsating flow, the overall heat transfer coefficient

increases with increasing the amplitude and decreases

with increasing the frequency and Prandtl number.

The effect of many parameters on time average

Nusselt number was numerically studied by [17, 19, 20

and 21]. It is reported that the increase of Nusselt number

depends on the value of the pulsation frequency and its

amplitude. With amplitude less than unity, pulsation has

no effect on time averaged Nusselt number [20]. In the

thermally fully developed flow region, a reduction of the

local Nusselt number was observed with pulsation of small

amplitude. However, with large amplitude, an increase in

the value of Nusselt number was noticed.

In summary, the time-average Nusselt number of

a laminar pulsating internal flow may be higher or lower

than that of the steady flow one, depending on the

frequency. The discrepancies of heat transfer rate from

that of the steady flow is increased as the velocity ratio ()

is increased. For hydro dynamically and fully developed

laminar pulsating internal flow, the local heat transfer rate

in the axial locations for X/D < Re/20 2 can be obtained

based on a quasi-steady flow [2].

Numerical investigations on turbulent pulsating flow have

been carried out by several researchers [22, 23 and 24]. It

is reported that there is an optimum Womersly number at

which the rate of heat transfer is enhanced [22 and 23]. In

pulsating turbulent flow through an abrupt pipe

expansion, Said et al. [24] reported that the %age

enhancement in the rate of heat transfer of about 10 was

observed for fluids having a Prandtl number less than

unity. Experimental investigations on pulsating turbulent

pipe flow have been conducted by many authors The

results showed an increase and reduction in the mean

Nusselt number with respect to that of the steady flow.

3. Experimental Investigation

Calculation of Heat Transfer Coefficient Experimental)

at upstream flow:

Results obtained by experimental set up For

upstream air flow at heat input of 98.98 watts (1350

/2), manometer water column difference of 40 mm,

pulsation motor speed is 100 RPM.

= (2+3+4+5)/4

= (1+6)/2

= h A (- a),

Where =

=

h = Q/ [A*()]

Calculation of Heat Transfer Coefficient (Theoretical)

by Correlation Method By correlation method at

temp

Discharge through orifice =

Where = 0.65,

is the area of orifice

= ( h ) /

( air)

= = 2.191032.54 = 4.46 /

= = 4.460.02519.80106 =11470.54

is kinematic viscosity obtained from data hand

book properties of air which is 19.80106 =11470.54

based on no correlation has been chosen that is Dittus-

Boelter equation

= . ..

We know = h/k,

Where h is heat transfer coefficient,

D is pipe inner diameter and

k is thermal Conductivity of air at mean

temperature obtained from properties.

=h

h = ( * )/

Calculation of Pulsation Frequency

Pulsation Frequency (f) = 2N/60

4. Results and Discussions:



The effect of pulsation on the heat transfer

characteristics are presented in terms of both relative

local and relative mean Nusselt number and heat transfer

coefficient for pulsated flow to the corresponding ones for

steady flow at the same Reynolds numbers. The local heat

transfer coefficient and Nusselt number is calculated by

varying length of tube by considering location of

thermocouples.

Calculation of Mean Thermal Characteristics for

upstream flow

Comparison between Experimental and Theoretical

Heat transfer coefficient with and without Pulsation

Graphs showed that the value of heat transfer coefficient

calculated by experimental and theoretical method is

similar. From this graphs it is proved that experimental

setup is validated.

Figure 2 Comparison of heat transfer coefficient

calculated experimentally and theoretically

Fig. 2 shows that the value of mean heat transfer

coefficient either increased or decreased with increasing

the value of Reynolds number.


Nusselt Number with and without Pulsation

Figure 3 Comparison of Nusselt Number calculated

experimentally and theoretically without Pulsation

Fig. 3 shows that the values of mean Nusselt number are

similar to each other without pulsation with increasing the

value of Reynolds number.


Heat Transfer coefficient at Pulsation frequency is

3.33

Figure 4 Comparison of Heat Transfer Coefficient

experimental and theoretical when (f= 3.33 Hz)

Fig. 4 shows that the value of mean heat transfer

coefficient calculated by experimentally and theoretically

either increased or decreased with increasing the value of

Reynolds number.


Nusselt Number at Pulsation frequency is 3.33



Figure 5 Comparison of Nusselt Number when

frequency is 3.33 calculated experimentally and

theoretically


similar to each other when pulsation frequency is 3.33 Hz

with increasing the value of Reynolds number.

Variations in Heat Transfer Coefficient with Reynolds

Number at diff pulsation Frequencies

For increment in pulsation frequency, it can be seen from

Fig. 6 that enhancement is found in mean heat transfer

coefficient in comparison of with and without pulsation.

Fig. 6 shows that the values of mean heat transfer

coefficient are either increases or decreases with

increasing both the value of Reynolds number and

pulsation frequencies.

Figure 6 Variations in Heat Transfer Coefficient with

Reynolds Number at various pulsation Frequencies

Variations in Nusselt Number with Reynolds Number at

diff pulsation Frequencies


Fig. 7 that enhancement is found in mean Nusselt Number

in comparison of with and without pulsation. Fig. 7 shows

that the values of mean Nusselt number are either

increases or decreases with increasing both the value of

Reynolds number and pulsation frequencies.

Figure 7 Variations in Nusselt Number with Reynolds

Number at various pulsation Frequencies

Calculation of Local Thermal Characteristics for

upstream flow

When Tube length is 50mm

Variations in Heat Transfer Coefficient with Reynold

Number at diff pulsation Frequencies when L=50mm


Fig. 8 that enhancement is found in mean heat transfer

coefficient in comparison of with and without pulsation

when tube length is considered is 50mm.

Fig. 8 shows that the values of mean heat transfer

coefficient are either increases or decreases with

increasing both the value of Reynolds number and

pulsation frequencies.



Figure 8 Variations in Heat Transfer Coefficient with

Reynolds Number at various pulsation Frequencies

when tube length is 50mm

Variations in Nusselt Number with Reynolds Number at

diff pulsation Frequencies when L=50mm


Fig. 9 that enhancement is found in mean Nusselt Number

in comparison of with and without pulsation.


either increases or decreases with increasing both the

value of Reynolds number and pulsation frequencies.

Figure 9 Variations in Nusselt number with Reynoldss

Number at various pulsation Frequencies when Tube

length is 50mm

5 Conclusions

The pulsation mechanism is designed by using variation in

pulsation motor speed. Conclusions from studied

experiment are as follows,

a) Higher values of the local heat transfer coefficient

occurred in the entrance of the tested tube. The

variation is more pronounced in the entrance

region than that in the downstream fully

developed region.

b) Value of heat transfer coefficient calculated by

experimental and theoretical method is similar.

From this experimental setup is validated.

c) The values of mean heat transfer coefficient are

increases if pulsation is created in flow of air.

d) The value of local Heat transfer coefficient either

increased or decreased with increasing the value

of Reynolds number and pulsation frequency.

e) The values of mean Nusselt number are increases

if pulsation is created in flow of air.

f) The value of local Nusselt number either

increased or decreased with increasing the value

of Reynolds number and pulsation frequency.

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